Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory – Pyramid (5079 m a.s.l.) (original) (raw)
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Journal of Geophysical Research, 2006
Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high altitude station, Manora Peak in Central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of Central Himalayas, and having a monthly mean AOD (at 500 nm) of 0.059 0.033 (typical to this site), total suspended particulate (TSP) concentration was in the range 15 -40 g m -3 (mean value 27.1 8.3 g m -3 ). Interestingly, aerosol BC had a mean concentration of 1.36 0.99 g m -3 , contributed to ~5.0 1.3% to the composite aerosol mass.
Atmospheric Chemistry and Physics, 2010
Aerosol optical properties have been analyzed through the ground-based Aerosol Robotic Network (AERONET) over the mega city Karachi during August 2006-July 2007. The aerosol optical depth (AOD) is strongly dependent on wavelength; for shorter wavelengths AOD values are higher than at longer wavelengths. The results reveal that the monthly average AOD at 500 nm ranges from 0.31 to 0.92 with an annual mean of 0.48± 0.18 and monthly averaged angstrom exponent (Alpha) ranges from 0.17 to 1.05 with an annual mean of 0.49± 0.31. The maximum monthly average AOD value of 0.92± 0.28 with the corresponding Alpha value of 0.21± 0.11 is found for July 2007, while the minimum monthly average AOD value of 0.31 ± 0.11 with the corresponding Alpha value of 0.53± 0.13 is recorded for March 2007. The volume size distribution in the coarse mode is higher in summer and lower in winter, whereas in the accumulation mode the volume size distribution is higher in winter than in other seasons due to the hygroscopic growth of aerosol particles. The single scattering albedo (SSA) during spring, autumn and summer seasons shows a slight increase with the wavelength and ranges from 0.88± 0.02 to 0.97± 0.01. The asymmetry parameter (ASY) is also wavelength dependent and varies from 0.61± 0.03 to 0.74± 0.02 during the year. The aerosol radiative forcing (ARF) for the whole observation period at the top of the atmosphere (TOA) is in the range of −7 to −35 Wm −2 (average −22± 6 Wm −2 ), at the surface from −56 to −96 Wm −2 (average −73± 12 Wm −2 ), increasing the atmospheric forcing from +38 to +61 Wm −2 (average +51± 13 Wm −2 ). The SBDART-AERONET radiative forcing at the surface and TOA agree with correlation of 0.92 and 0.82, respectively.
Investigation of Aerosol Climatology and Long-Range Transport of Aerosols over Pokhara, Nepal
Atmosphere
This study presents the spectral monthly and seasonal variation of aerosol optical depth (τAOD), single scattering albedo (SSA), and aerosol absorption optical depth (AAOD) between 2010 and 2018 obtained from the Aerosol Robotic Network (AERONET) over Pokhara, Nepal. The analysis of these column-integrated aerosol optical data suggests significant monthly and seasonal variability of aerosol physical and optical properties. The pre-monsoon season (March to May) has the highest observed τAOD(0.75 ± 0.15), followed by winter (December to February, 0.47 ± 0.12), post-monsoon (October and November, 0.39 ± 0.08), and monsoon seasons (June to September, 0.27 ± 0.13), indicating seasonal aerosol loading over Pokhara. The variability of Ångström parameters, α, and β, were computed from the linear fit line in the logarithmic scale of spectral τAOD, and used to analyze the aerosol physical characteristics such as particle size and aerosol loading. The curvature of spectral τAOD, α’, computed f...
Study of Aerosol Optical Properties Over Two Sites in the Foothills of the Central Himalayas
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Atmospheric aerosol possesses impacts on climate system and ecological environments, human health and agricultural productivity. The environment over Himalayas and Tibetan Plateau region are continuously degraded due to the transport of pollution from the foothills of the Himalayas; mostly the Indo-Gangetic Plain (IGP). Thus, analysis of aerosol optical properties over two sites; Lumbini and Kathmandu (the southern slope of central Himalayas) using AERONET’s CIMEL sun photometer were conducted in this study. Aerosol optical depth (AOD at 500 nm), angstrom exponent (α or AE), volume size distribution (VSD), single scattering albedo (SSA) and asymmetry parameter (AP) were studied for 2013–2014 and the average AOD was found to be: 0.64 ± 0.41 (Lumbini) and 0.45 ± 0.30 (Kathmandu). The average AE was found to be: 1.25 ± 0.24 and 1.26 ± 0.18 respectively for two sites. The relation between AO...
Meteorology and Atmospheric Physics, 2011
The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.9ºN, 77.12ºE) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Δ τ pλ = ±0.05 ± 0.15 τ pλ ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surface-reaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day-1, respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.
Meteorology and …, 2011
The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.98N, 77.128E) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Å ngström exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Ds pk = ±0.05 ± 0.15s pk ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surfacereaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day -1 , respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.
Atmospheric Chemistry and Physics, 2014
The Himalaya mountains along the southern edge of the Tibetan Plateau act as a natural barrier for the transport of atmospheric aerosols from the polluted regions of South Asia to the main body of the Tibetan Plateau. In this study, we investigate the seasonal and diurnal variations of aerosol optical properties measured at two Aerosol Robotic Network (AERONET) sites on the southern side of the Himalaya (Pokhara 812 m above sea level (a.s.l.) and EVK2-CNR, 5079 m a.s.l. in Nepal) and one on the northern side (Qomolangma (Mt. Everest) station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS_CAS) in Tibet, 4076 m a.s.l. in China). While observations at QOMS_CAS and EVK2-CNR can generally be representative of a remote background atmosphere...
Altitude variation of aerosol properties over the Himalayan range inferred from spatial measurements
Journal of Atmospheric …, 2011
Altitude variations of the mass concentration of black carbon, number concentration of composite aerosols are examined along with the columnar spectral aerosol optical depths using state of the art instruments and theÅngström parameters are inferred from the ground based measurements at several altitude levels, en route from Manora Peak, Nainital ( $ 1950 m above mean sea level) to a low altitude station Haldwani ($ 330 m above mean sea level) at its foothill within an aerial distance of o 10,000 m. The measurements were done during the winter months (November-February) of 2005, 2006 and 2007 under fair weather conditions. The results show a rapid decrease in all the measured parameters with increase in altitude, with 460% contribution to the AOD coming from the regions below $ 1000 m. TheÅngström wavelength exponent remained high in the well mixed region, and decreased above. The normalized AOD gradient was used to estimate aerosol mixing height, which was found to be in the altitude range 1000-1500 m, above which the particle concentrations are slowly varying as a function of altitude. The heating rate at the surface is found to be maximum but decreases sharply with increase in altitude. Analysis of the wavelength dependence of absorption aerosol optical depth (AAOD) showed that the aerosol absorption over the site is generally due to mixed aerosols.
Atmósfera, 2012
Las observaciones de un radiómetro de longitud de onda múltiple (MWR, por sus siglas en inglés) ubicado en tierra en el valle Kullu en la región noroccidental del Himalaya, de abril de 2007 a marzo de 2008, muestran que la profundidad óptica espectral del aerosol (AOD, por sus siglas en inglés) y el coeficiente Ångstr?m de turbidez (β) son altos durante la estación del monzón, ligeramente menores en el verano, bajos en invierno y los más bajos en otoño, para días claros, neblinosos y parcialmente claros, mientras que el exponente Ångstr?m de longitud de onda (α) tiene una tendencia opuesta. Los valores promedio anuales de AOD a 5000 nm son 0.25 ± 0.01, 0.46 ± 0.02 y 0.28 ± 0.02, para días de cielos claros, nebulosos y parcialmente claros, respectivamente. Los valores correspondientes para β son 0.13 ± 0.01, 0.22 ± 0.01 y 0.15 ± 0.01 y los de α 1.09 ± 0.04, 1.18 ± 0.03 y 0.89 ± 0.05. La α es ligeramente mayor pero la β es considerablemente más alta en los días nebulosos que en los claros, indicando que la niebla montañosa es rica en partículas gruesas. Hay una buena concordancia entre los valores MWR y los AOD satelitales de MODIS, con coeficientes de correlación anuales de 0.89, 0.70 y 0.81 para días claros, nebulosos y parcialmente claros, respectivamente. La correlación entre AOD a 500 nm y el coeficiente β con la temperatura, velocidad del viento y humedad es significativamente positivo, mientras que el del exponente α es negativo para la mayoría de los días, lo que sugiere alto AOD y turbidez pero baja concentración de partículas finas en días calientes, húmedos y con viento y viceversa. Asimismo, la correlación entre AOD a 500 nm y el coeficiente β con la dirección del viento es la mayoría de las veces negativa, mientras que la del exponente α es positiva, indicando que AOD y la turbidez disminuyen pero la concentración de partículas finas aumenta al cambiar la dirección del viento más hacia el sur de nuestro sitio. Así, durante el periodo analizado, los vientos que se dirigen hacia nuestro sitio desde las planicies indogangéticas son ricos en partículas gruesas, mientras que los vientos de la dirección sur o del desierto Thar transportan principalmente partículas finas. 200 N. L. Sharma et al.